diff --git a/src/czml3/properties.py b/src/czml3/properties.py
index 5a7779e..4cb298f 100644
--- a/src/czml3/properties.py
+++ b/src/czml3/properties.py
@@ -366,6 +366,7 @@ def checks(self):
                     self.cartographicDegrees,
                     self.cartographicRadians,
                     self.cartesianVelocity,
+                    self.reference,
                 )
             )
             != 1
@@ -421,7 +422,9 @@ class ViewFrom(BaseCZMLObject, Interpolatable, Deletable):
 
     See `here <https://github.com/AnalyticalGraphicsInc/czml-writer/wiki/ViewFrom>`__ for it's definition."""
 
-    cartesian: None | Cartesian3Value | list[float] | TimeIntervalCollection = Field()
+    cartesian: None | Cartesian3Value | list[float] | TimeIntervalCollection = Field(
+        default=None
+    )
     """The offset specified as a three-dimensional Cartesian value [X, Y, Z].  See `here <https://github.com/AnalyticalGraphicsInc/czml-writer/wiki/Cartesian3Value>`__ for it's definition."""
     reference: None | ReferenceValue | str | TimeIntervalCollection = Field(
         default=None
@@ -442,6 +445,16 @@ def validate_reference(cls, r):
             return ReferenceValue(value=r)
         return r
 
+    @model_validator(mode="after")
+    def checks(self):
+        if self.delete:
+            return self
+        if self.cartesian is None and self.reference is None:
+            raise ValueError(
+                "ViewFrom must have either 'cartesian' or 'reference' specified"
+            )
+        return self
+
 
 class Billboard(BaseCZMLObject):
     """A billboard, or viewport-aligned image. The billboard is positioned in the scene by the position property. A billboard is sometimes called a marker.
diff --git a/tests/test_properties.py b/tests/test_properties.py
index 2c65d23..cf2ca3a 100644
--- a/tests/test_properties.py
+++ b/tests/test_properties.py
@@ -752,35 +752,21 @@ def test_position_cartographic_degrees():
 
 def test_position_reference():
     expected_result = """{
-    "cartesian": [
-        0.0,
-        0.0,
-        0.0
-    ],
     "reference": "this#satellite"
 }"""
-    pos = Position(cartesian=[0, 0, 0], reference="this#satellite")
+    pos = Position(reference="this#satellite")
     assert str(pos) == expected_result
-    pos = Position(
-        cartesian=[0, 0, 0], reference=ReferenceValue(value="this#satellite")
-    )
+    pos = Position(reference=ReferenceValue(value="this#satellite"))
     assert str(pos) == expected_result
 
 
 def test_viewfrom_reference():
     expected_result = """{
-    "cartesian": [
-        1.0,
-        1.0,
-        1.0
-    ],
     "reference": "this#satellite"
 }"""
-    v = ViewFrom(reference="this#satellite", cartesian=[1.0, 1.0, 1.0])
+    v = ViewFrom(reference="this#satellite")
     assert str(v) == expected_result
-    v = ViewFrom(
-        reference=ReferenceValue(value="this#satellite"), cartesian=[1.0, 1.0, 1.0]
-    )
+    v = ViewFrom(reference=ReferenceValue(value="this#satellite"))
     assert str(v) == expected_result
 
 
@@ -808,7 +794,7 @@ def test_viewfrom_has_delete():
 
 def test_viewfrom_no_values_raises_error():
     with pytest.raises(ValidationError) as _:
-        ViewFrom()  # type: ignore
+        ViewFrom()
 
 
 def test_single_interval_value():
@@ -1156,13 +1142,14 @@ def test_tileset():
 
 def test_check_classes_with_references_ViewFrom():
     assert (
-        str(ViewFrom(cartesian=[0, 0, 0], reference="this#that"))
+        str(ViewFrom(reference="this#that"))
+        == """{
+    "reference": "this#that"
+}"""
+    )
+    assert (
+        str(ViewFrom(reference=ReferenceValue(value="this#that")))
         == """{
-    "cartesian": [
-        0.0,
-        0.0,
-        0.0
-    ],
     "reference": "this#that"
 }"""
     )
@@ -1204,13 +1191,8 @@ def test_check_classes_with_references_ArcType():
 
 def test_check_classes_with_references_Position():
     assert (
-        str(Position(cartesian=[0, 0, 0], reference="this#that"))
+        str(Position(reference="this#that"))
         == """{
-    "cartesian": [
-        0.0,
-        0.0,
-        0.0
-    ],
     "reference": "this#that"
 }"""
     )
@@ -1515,6 +1497,26 @@ def test_position_bad_cartesianVelocity():
         Position(cartesianVelocity=[])
 
 
+def test_position_bad_multipleTypes():
+    with pytest.raises(TypeError):
+        Position(cartesian=[0], reference=ReferenceValue(value="1#this"))
+    with pytest.raises(TypeError):
+        Position(cartographicRadians=[0], reference=ReferenceValue(value="1#this"))
+    with pytest.raises(TypeError):
+        Position(cartographicDegrees=[0], reference=ReferenceValue(value="1#this"))
+    with pytest.raises(TypeError):
+        Position(cartesianVelocity=[0], reference=ReferenceValue(value="1#this"))
+
+    with pytest.raises(TypeError):
+        Position(cartesian=[0], reference="1#this")
+    with pytest.raises(TypeError):
+        Position(cartographicRadians=[0], reference="1#this")
+    with pytest.raises(TypeError):
+        Position(cartographicDegrees=[0], reference="1#this")
+    with pytest.raises(TypeError):
+        Position(cartesianVelocity=[0], reference="1#this")
+
+
 def test_no_values():
     with pytest.raises(ValueError):
         Color(rgba=[])